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TUESDAY, May 1, 2012 — What affects 50 million Americans and is the most common cause of disability in the United States?

It's arthritis, which encompasses not only osteoarthritis — the "wear-and-tear" type that affects many of us as we age — but also rheumatoid arthritis, fibromyalgia, gout, and juvenile arthritis, among other painful conditions. And just in time for the start of Arthritis Action Month, there are some new figures detailing how many of us are living with chronic pain.

The Gallup-Healthways Well-Being Index asked more than 350,000 U.S. adults whether they had pain in their knee, leg, neck, or back, or elsewhere in the body. Nearly half (47 percent) had at least one of these common types of pain, and 7 percent said they had pain in all of these areas. The incidence of pain also went up with age, with more than a third of those over 50 saying they had some sort of back, neck, knee, or leg problem, and nearly a fourth reporting they had some other condition that caused pain.

Weight, Pain, and Arthritis

The poll also found that people who made less than $36,000 a year were more likely to say they had chronic pain, which the researchers speculate may have been because of lack of health insurance or working in manual jobs. But there was another factor: The lower-income respondents were more likely to be carrying excess weight. Overall, 36 percent of obese Americans polled had knee or leg pain, and 37 percent had neck or back pain; 24 percent had some other type of pain.

Although the Gallup-Healthways poll didn't ask specifically about arthritis, previous research has highlighted the connection between the growing numbers of people with this condition and the obesity epidemic. According to a 2011 report from the Centers for Disease Control and Prevention, obesity prevalence is 54 percent higher in American adults with arthritis compared with those who don't have arthritis. Besides putting stress on joints, extra pounds are also linked to inflammation, a factor in rheumatoid arthritis and osteoarthritis. A recent study found that for women, there was a strong connection between rheumatoid arthritis and being overweight or obese.

If weight loss seems daunting, remember that even small decreases can help ease arthritis pain: One study found that for each pound of body weight lost, four pounds of pressure are taken off the knee.